The two countries are natural partners. Both are U.S. allies, democratic societies, and share similar values and security concerns. During the Cold War, both Japan and South Korea feared expansion of communism from the Soviet Union and China, and a North Korean invasion of the South. Today, both face the North Korean nuclear threat and share mutual concern about the rise of China. In addition to common interests, Japan and Kroea share similar customs, culture, and language. All these suggest that it is logical and desirable for the two countries to have a strong and cooperative bilateral relationship.